The stick placement apparatus of the present invention is the subject of prior U.S. Pat. Nos. 4,253,787 and 4,324,521, the disclosures of which are incorporated herein by reference.
Lumber that is produced from logs contains moisture that is undesirable. If allowed to dry naturally, the lumber pieces can warp and or split. This can be greatly alleviated by controlled drying. Thus the lumber is formed into tiers and the tiers into stacks that are placed in a dry kiln for controlled drying of the lumber. Very generally, the lumber pieces are conveyed on conveyors to a stacker whereat tiers of lumber pieces are placed one on top of the other by stacking forks. An automatic stick placer apparatus spaces sticks between each tier to allow air to flow freely around each tier of lumber pieces within the dry kiln.
As indicated above the apparatus for automatically placing the sticks between the tiers is described in the mentioned commonly assigned patents. Basically a conveyor conveys sticks in a desired spaced apart relation below a series of sticker forks which sequentially receives the lumber tiers and transfers the lumber tiers from the lumber conveyor to an adjacent stack. The stacker forks oscillate back and forth between the conveyor and the stack. Each fork carries a stick holding pan. A stick transfer device in coordination with stacker forks picks the sticks off the stick conveyor and places them into the holding pans adjacent each fork, just as the forks engage and transfer a tier of lumber pieces. Thus the stickers and tier of lumber pieces are simultaneously placed on the stack by the stacker forks.
The stick transfer mechanism essentially comprises multiple pairs of arms, each pair of arms operating to lift a stick off the stick conveyor and place it in a pan adjacent a fork. The timing is important as the process rapidly cycles through one stacking motion after another. The sticks have to be spaced properly and located at the right position in order for the rapidly cycled stick transfer arms to raise up under a stick and transfer the stick into position in the pan. Although the mechanism is very accurate and miscues are infrequent, occasionally a stick will shift out of it's required position on the conveyor and cause a jamming of the equipment. In such event it is likely that a stick transfer arm will become damaged. Most likely it is the lifting tip portion of the arm that gets broken or bent but on occasion the main arm structure will also be damaged.
Replacing a stick transfer arm is a fairly major repair project and requires substantial down time, a major concern for the stacking process. Any such interruption in the lumber processing operation can be very costly and is to be avoided if possible.